1. Field of the Invention
The present invention relates to an electronic device, apparatuses employing the device such as an electronically controlled mechanical clock, and a method of controlling such a device and apparatuses. The device and clock of the present invention include a mechanical energy source; an electric power generator, driven by the mechanical energy source, for generating electric power by induction and supplying resulting electrical energy; and a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator.
2. Description of the Related Art
Japanese Examined Patent Publication No. 7-119812 is directed to an electronically controlled mechanical clock in which mechanical energy generated when a spring is released is converted to electrical energy using an electric power generator. A rotation controller is driven by the electric energy so as to control a current flowing through a coil of the electric power generator so that the clock hands connected to a wheel train are precisely driven to indicate precise time.
To operate such an electronically controlled mechanical clock for a long period of time, it is important to increase braking torque when the spring torque is large without causing a reduction in generated electric power. That is, in electronically controlled mechanical clocks, it is desirable to prioritize the braking torque applied to the electric power generator versus the electric power generated by the electric power generator, such that a higher priority is given to the braking torque when the spring torque is large, while a higher priority is given to the electric power when the spring torque is small because strong braking is not needed in this case.
As used herein, the expression xe2x80x9cwhen the torque is largexe2x80x9d or the like describes not only a state in which the spring torque is large because the spring is in a fully or sufficiently wound state, but also a state in which the driving torque applied to the rotor is increased due to a disturbance, such as vibration or mechanical shock. Similarly, the expression xe2x80x9cwhen the torque is lowxe2x80x9d or the like describes not only a state in which the spring torque is low because the spring is in a fully or nearly fully unwound/released state, but also a state in which the driving torque applied to the rotor is reduced due to a disturbance, such as vibration or mechanical shock.
In the technique disclosed in Japanese Examined Patent Publication No. 7-119812, a xe2x80x9cbraking-offxe2x80x9d angular range and a xe2x80x9cbraking-onxe2x80x9d angular range are provided in each revolution of a rotor. In each period of a reference signal, the rotational speed of the rotor is increased and a greater amount of electric power is generated in the braking-off angular range, while the rotational speed of the rotor is decreased by applying braking in the braking on angular range. That is, the rotational speed is controlled such that the generated electric power is increased during a high-speed period thereby compensating for the reduction in the electric power which occurs when the electric power generator is braked. The braking-off operation is performed at a plurality of first points of time in respective successive periods of the reference signal generated by a quartz oscillator or the like, and a braking-on operation is performed at a second point of time apart from the first point of time in each period of the reference signal.
However, in the technique of Japanese Examined Patent Publication No. 7-119812, a reduction in electric power generated by the electric power generator occurs when the electric power generator is braked, and thus there is a limitation in suppressing the reduction in the electric power when the braking torque is increased. This problem occurs not only in electronically controlled mechanical clocks, but also in other various electronic devices, such as music boxes, metronomes, and electric shavers, each of which include a part rotated by a mechanical energy source such as a spring or rubber. Thus, there is a need for a technique which can solve the above problem.
Another problem associated with the technique in Japanese Examined Patent Publication No. 7-119812, is that a braking-on operation started at a second point of time in a certain reference period is forcibly switched to a braking-off operation at a first point of time in the following reference period, regardless of the state in terms of rotation of the electric power generator. This can cause the braking amount to become insufficient depending on the state, and thus it takes a long time to reach a target rotational speed. Even if the braking operation is performed using a control signal, the operation is switched to a mode in which braking is performed in synchronization with a reference period, regardless of the period of the control signal. This can cause degradation in the braking control accuracy.
Thus, there is a need to control the braking operation in a more precise manner so as to achieve higher accuracy in the operation of various operating parts. Such control is needed not only in electronically controlled mechanical clocks, but also in other various electronic devices which have a part which is rotated by a mechanical energy source such as a spring or rubber. Other devices in which such control is needed include, for example, music boxes (i.e, drums thereof), metronomes (i.e., pendulums thereof), various electronic toys, and electric shavers.
Therefore, it is an object of the present invention to overcome the aforementioned problems.
It is another object of the invention to provide an electronic device, an electronically controlled mechanical clock, and a method of controlling such a device and clock, which allow a braking torque applied to an electric power generator to be increased without causing a significant reduction in electric power generated by the electric power generator. Unlike the technique in Japanese Examined Patent Publication No. 7-119812, the electric power generator is controlled using a chopping signal, so as to increase the applied braking torque without causing a significant reduction in electric power.
It is a further object of the invention to provide an electronic device, an electronically controlled mechanical clock, and a method of controlling such a device and clock, which allow a precise and large amount of braking torque to be applied during a braking operation using a chopping signal, thereby ensuring that the rotational speed is controlled in a quick and highly reliable manner.
The present invention is based on the discovery made by the inventors herein that when an electric power generator is controlled in a chopping manner by applying a chopping signal to a switch such that the switch connects the two terminals of the electric power generator in a closed-loop state in response to the chopping signal, the driving torque (i.e., braking torque, damping torque) increases with decreasing frequency and/or with increasing duty ratio of the chopping signal, while the charged voltage (i.e., generated voltage) corresponding to electric power generated by the electric power generator increases with increasing chopping signal frequency but does not greatly decrease with increasing duty ratio of the signal, and, on the contrary, at frequencies higher than 50 Hz, the charged voltage increases with increasing duty ratio in a range where the duty ratio is less than 0.8 as shown in FIGS. 32 to 35.
Thus, in one aspect, the present invention provides an electronic device comprising a mechanical energy source; an electric power generator, driven by the mechanical energy source, for generating electric power by induction and supplying electrical energy; and a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator. The rotation controller includes a switch capable of connecting two terminals of the electric power generator in a closed-loop state; a chopping signal generator for generating two or more types of chopping signals which are different in at least either duty ratio or frequency and which direct the rotation controller to apply a strong braking force to the electric power generator; and a chopping signal selector for selecting one of the chopping signals and applying it to the switch, thereby controlling the electrical power generator in a chopping manner according to the selected signal.
In such an electronic device, when the electric power generator is driven by the mechanical energy source such as a spring, the rotational speed of the rotor is controlled by applying a braking force to the electric power generator via the rotation controller.
The rotation of the electric power generator is controlled by applying a chopping signal to the switch which is capable of connecting two terminals of the electric power generator in a closed-loop state thereby turning the switch on and off. When the switch is closed in response to the chopping signal, the two ends of the coil of the electric power generator are electrically connected in the closed-loop state. As a result, the electric power generator is braked, and energy is stored in the coil of the generator. If the switch is opened, the loop is opened, and the electric power generator outputs electric power. In this state, the energy stored in the coil results in an increase in the output voltage. If a strong braking force is applied to the electric power generator using the chopping technique of the present invention, the reduction in the generated electric power due to the braking can be compensated for by the increase in the generated voltage which occurs when the switch is turned off (i.e., opened). Thus, the braking torque (braking force) can be increased without causing a significant reduction in the generated electric power. This makes it possible to realize an electronic device which can operate for a long period of time.
When a strong braking force is applied (in the strong braking mode), the chopping signal selector selects a chopping signal from the chopping signals which are different in at least either duty ratio or frequency and which are set for strong braking, and applies the selected chopping signal is applied to the switch. More specifically, when a large braking force is required (i.e., when a higher priority is to be given to braking) because the driving torque is large, a chopping signal, which provides a larger braking force, is applied to the switch. Conversely, when the driving torque becomes low and a large braking force is not necessary (i.e., when a higher priority is to be given to generation of electric power), a chopping signal is applied which does not provide a large braking force but which results in an increase in the charged voltage. This technique ensures that a proper braking force (braking torque) corresponding to the driving torque applied to the rotor of the electric power generator is applied to the electric power generator, thereby properly controlling the rotational speed of the electric power generator. Thus, the controllable operating range is increased, and the charged voltage can likewise be increased. This makes it possible to further increase the braking torque while more effectively suppressing the reduction in the generated electric power. Again, this makes it possible to realize an electric device which can operate for a longer period of time.
In the present invention, the closed-loop state, which is achieved when the switch is turned on, refers to a state that results in an increase in the braking force applied to the electric power generator. As long as this requirement is met, the closed-loop may include a resistor or the like disposed, for example, between the switch and the electric power generator. However, it is desirable to form the closed-loop state by directly connecting the two terminals of the electric power generator, because the voltages of the two terminals can be made equal more easily, thereby allowing the generator to be braked in a more efficient fashion. When the signal output from the chopping signal selector is applied to the switch, the signal may be applied either directly or indirectly via another circuit or device.
By applying braking forces with two or more different magnitudes, as described above, it is possible to generate a regulated voltage required for a system. This makes it possible to improve the stability of the system. Furthermore, it becomes possible to maximize the braking effect and the self-supporting capability of the system.
The two or more types of chopping signals may be equal in frequency but different in duty ratio. More specifically, the chopping signals may include a first chopping signal with a duty ratio in the range from 0.75 to 0.85 (13/16, for example), and a second chopping signal with a duty ratio in the range from 0.87 to 0.97 (15/16, for example). As shown in FIGS. 32 to 35, it is possible to change the charged voltage and the driving torque (braking torque) by changing the duty ratio of the chopping signal while maintaining the frequency at a fixed value. Therefore, when the braking force is more important than the generated electric power, the second chopping signal with a greater duty ratio is employed to obtain a greater braking torque. On the other hand, when the generation of electric power is more important, the first chopping signal with a duty ratio which is not very small (but smaller than the duty ratio of the second chopping signal) so as to achieve a large charged voltage. That is, the rotation of the electric power generator can be properly controlled by properly selecting the chopping signal depending on the state of the electric power generator. A specific example of a set of two or more types of chopping signals used for providing strong braking forces includes three different chopping signals with duty ratios of 15/16, 14/16, and 13/16, respectively. This allows the braking force and the generated electric power to be controlled in a finer fashion, thereby achieving further improvements in the stability of the system and the self-supporting capability.
It should be noted that in FIGS. 32 to 35, the term xe2x80x9cdriving torquexe2x80x9d may also be considered as xe2x80x9cbraking torque,xe2x80x9d because the driving torque refers to a torque which is balanced with a braking torque applied so as to obtain a desired rotational speed. Similarly, the term xe2x80x9ccharged voltagexe2x80x9d may also be considered as xe2x80x9cgenerated voltagexe2x80x9d because the voltage charged in a capacitor results from the voltage generated by the electric power generator.
Instead of fixing the frequency but varying the duty ratio among the chopping signals, the two or more types of chopping signals described above may be equal in duty ratio but different in frequency. More specifically, the two or more types of chopping signals may include a first chopping signal with a frequency in the range from 110 to 1100 Hz (512 Hz, for example), and a second chopping signal with a frequency in the range from 25 to 100 Hz (64 Hz, for example). As shown in FIGS. 32 to 35, it is possible to change the charged voltage and the driving torque (braking torque) by changing the frequency of the chopping signal while maintaining the duty ratio at a fixed value. Therefore, when the braking force is more important than the generated electric power, the second chopping signal with a lower frequency is employed to obtain a greater braking torque. On the other hand, when the generation of electric power is more important, the first chopping signal with a higher frequency is employed to obtain a greater charged voltage. That is, the rotation of the electric power generator can be properly controlled by properly selecting the chopping signal depending on the state of the electric power generator. As can be seen from FIGS. 32 to 35, when the frequency is varied, it becomes possible to change the charged voltage and the braking torque over greater ranges, as compared to the case where only the duty ratio is varied. Thus, the controllable operating range can be expanded.
In FIGS. 32 and 33, the driving torque and the charged voltage are plotted as a function of the duty ratio for five different frequencies, 25, 50, 100, 500, and 1000 Hz. In FIGS. 34 and 35, the driving torque and the charged voltage are plotted as a function of the duty ratio for six different frequencies, 32, 64, 128, 256, 512, and 1024 Hz. In each case, the results are obtained by measuring the charged voltage across the capacitor (the voltage generated by the electric power generator) and the driving torque while maintaining the duty ratio at a fixed value, as will be described later.
Another variation is that the two or more types of chopping signals described above may be different in both duty ratio and frequency. More specifically, the two or more types of chopping signals may include a first chopping signal having a duty ratio in the range from 0.75 to 0.85 and having a frequency in the range from 110 to 1100 Hz, and a second chopping signal having a duty ratio in the range from 0.87 to 0.97 and having a frequency in the range from 25 to 100 Hz. The specific frequencies of the chopping signals may be selected depending on the signal generation capability of a specific electronic device. For example, in the case of a clock including a quartz resonator, signals obtained by dividing the frequency of a signal generated by the quart resonator may be employed. This technique is very efficient, because it is not required to additionally generate chopping signals. In other types of electronic devices, if there are particular frequencies which can be easily generated, they can be employed. By controlling the rotation of the electric power generator in a chopping fashion using chopping signals which are different in both duty ratio and frequency, it becomes possible to control the braking force in a very effective fashion.
More specifically, if the braking force is more important, the second chopping signal having a low frequency (64 Hz, for example) and having a large duty ratio (15/16, for example) may be employed to apply a strong braking force. This allows the braking force to be further increased, thereby controlling the rotational speed in a more reliable fashion. As can be seen from FIGS. 32 to 35, the braking torque can be increased by decreasing the frequency of the chopping signal and increasing the duty ratio. Thus, by employing a chopping signal meeting these requirements, a great braking torque can be obtained.
On the other hand, if the generation of electric power is more important, the first chopping signal having a high frequency (512 Hz, for example) and having a large duty ratio (13/16, for example) may be employed to obtain a proper braking force corresponding to the driving torque and to also obtain a large charged voltage. As can be seen from FIGS. 32 to 35, the charged voltage can be increased by increasing the frequency while setting the duty ratio in the range from 0.75 to 0.85. The first chopping signal described above meets these requirements.
If chopping signals differing in both frequency and duty ratio are employed, it is possible to control the charged voltage and the braking torque over greater ranges, as compared to the case where only the frequency or the duty ratio is varied. Thus, the controllable operating range can be expanded, and the rotational speed can be controlled in a more efficient fashion.
As described above, when two or more types of chopping signals having the same frequency are used for strong braking, the chopping signal having the greater duty ratio is employed when the braking torque is more important, and the chopping signal having the smaller duty ratio is employed when the charged voltage is more important, thereby ensuring that the rotational speed is controlled in a very efficient fashion.
When two or more types chopping signals having the same duty ratio are used for strong braking, the chopping signal having the lower frequency is employed when the braking torque is more important, and the chopping signal having the higher frequency is employed when the charged voltage is more important, thereby ensuring that the rotational speed is controlled in a very efficient fashion.
Preferably, the rotation controller described above includes a priority determination circuit that determines the priority of applying a braking torque to the electric power generator versus the priority of generating electric power with the generator. In the case where the priority determination circuit determines that a higher priority should be given to the braking torque, the chopping signal selector selects from the two or more types of chopping signals an appropriate chopping signal and applies the selected chopping signal to the switch. Such a chopping signal will have a large duty ratio when frequency is fixed, a low frequency when duty ratio is fixed, or a both of these characteristics when neither is fixed. However, if the priority determination circuit determines that a higher priority should be given to the electric power, the chopping signal selector selects a chopping signal with either a small duty ratio (when frequency is fixed), a high frequency (when duty ratio is fixed), or a chopping signal having both of these characteristics (when neither is fixed), and applies the selected chopping signal to the switch.
For determining the priority of applying braking torque to the electric power generator versus the priority of generating electric power with the generator, the priority determination circuit may include a voltage detector that detects the voltage generated by the electric power generator, a rotation period detector that detects the rotation period of the electric power generator, or a braking amount detector that detects the amount of braking applied to the electric power generator. By switching the chopping signal in the strong braking mode in accordance with data representing one of these parameters using the priority determination circuit, it is possible to select an optimum chopping signal, depending on the required braking force, and thus the rotational speed can be controlled in an effective fashion.
The chopping signal selector may select and apply a chopping signal to the switch in the strong braking mode from the two or more chopping signals set for strong braking, in accordance with the voltage generated by the electric power generator. Alternatively, the rotation controller may include an up/down counter which receives, at its up count input, a rotation detection signal generated based on the rotation period of the electric power generator and which also receives, at its down count input, a reference signal. In this case, the chopping signal selector selects and applies an appropriate chopping signal set for strong braking, in accordance with the value of the up/down counter. Alternatively, the chopping signal selector may select and apply a chopping signal in the strong braking mode, in accordance with a braking amount represented by the ratio of a braking period to one period of a reference signal. By switching/applying the chopping signal in the strong braking mode in accordance with data representing one of these parameters, it is possible to select an optimum chopping signal depending on the required braking force, and thus the rotational speed can be controlled in an effective fashion.
It is desirable that the rotation controller be capable of applying not only the strong braking force but also a weak braking force to the electric power generator, such that, when the weak braking force is applied to the electric power generator, the rotation controller applies a chopping signal with a duty ratio smaller than the duty ratio of any of the chopping signals set for strong braking. In the weak braking mode, a chopping signal with a very small duty ratio (1/16, for example) may be employed so that a very small braking force is applied to the electric power generator. The frequency of the chopping signal for weak braking may or may not be equal to that of the strong braking.
When a strong braking force is not applied, a chopping signal with a small duty ratio in the range, for example, from 0.01 to 0.30 may be applied to the switch, thereby applying a weak braking force to the electric power generator, or the switch may be maintained in an open state so that no braking force is applied to the electric power generator. By applying such a chopping signal to the switch in the weak braking mode, it becomes possible to decrease the driving torque while maintaining the charged voltage to a certain level. That is, it is possible to increase the charged voltage to a certain degree even in the weak braking mode.
It is even more desirable, in the weak braking mode, that a chopping signal with a duty ratio in the range from 0.01 to 0.15 be applied to the switch thereby controlling the electric power generator in a chopping fashion. Still more desirably, a chopping signal with a duty ratio in the range from 0.05 to 0.10 is applied. By applying a chopping signal with a duty ratio in the range from 0.01 to 0.15 to the switch in the weak braking mode, it is possible to reduce the driving torque while maintaining the charged voltage to a certain level. This allows the control in the weak braking mode to be performed in an effective fashion. If a chopping signal with a duty ratio in the range from 0.05 to 0.10 is employed, it becomes possible to reduce the braking torque while achieving a greater charged voltage. That is, the control in the weak braking mode can be performed in a more effective fashion.
The frequency of the chopping signal having a duty ratio in the range from 0.01 to 0.30 may be set to a value within the same range as that employed in the strong braking mode. As can be seen from FIGS. 32 to 35, when the duty ratio is small, the braking force and the generated electric power do not greatly depend on the frequency, and thus the frequency may be equal to that employed in the strong braking mode.
It is desirable that the chopping signal frequency at which the switch is turned on and off by the rotation controller be 3 or more times greater than the frequency of a voltage waveform which is generated when the rotor of the electric power generator rotates at a set speed. More desirably, the chopping signal frequency is 3 to 150 times greater than the frequency of the generated voltage waveform, and most desirably the chopping signal frequency is 5 to 130 times greater than the frequency of the generated voltage waveform.
Usually, if the chopping frequency is lower than 3 times the frequency of the generated voltage waveform, the voltage cannot be effectively increased. On the other hand, if the chopping frequency is greater than 150 times the frequency of the generated voltage waveform, integrated circuit electric power consumption increases in the chopping operation. That is, much electric power is consumed when electric power is generated. Thus, it is desirable that the chopping frequency be lower than 150 times the frequency of the generated voltage waveform. When the chopping frequency is within the range 3 to 150 times the frequency of the generated voltage waveform, the rate of change of the torque with respect to the change in the duty cycle becomes constant. This makes it easy to control the torque. However, depending on a specific application or control scheme, the chopping frequency may be set to a value lower than 3 times or greater 150 times the frequency of the generated voltage waveform.
Specifically, the chopping signal frequency may be set to a value in the range from 25 Hz to 1100 Hz. More desirably, the chopping signal frequency may be set to a value in the range from 64 Hz to 512 Hz. The switch which is turned on and off by the chopping signal may be formed of a field effect transistor. In this case, the gate capacitance of the transistor results in an increase in power consumption when the switching frequency becomes high. To minimize the power consumption, it is desirable that the chopping signal frequency be equal to or lower than 512 Hz. However, the maximum allowable power consumption depends on specific electronic devices, and the chopping signal frequency may be set to a value equal to or lower than about 1100 Hz to achieve high performance in terms of the braking performance or the electric power generation performance. On the other hand, if the chopping signal frequency is low, the charged voltage decreases. From this point of view, it is desirable to set the chopping signal frequency to 25 Hz or higher, and more desirably to 64 Hz or higher.
According to another aspect of the present invention, there is provided an electronic device comprising a mechanical energy source; an electric power generator, driven by the mechanical energy source, for generating electric power by induction and supplying electrical energy; a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator. The rotation controller comprises a switch capable of connecting two terminals of the electric power generator into a closed-loop state; a chopping signal generator that generates two or more types of chopping signals which are different in at least either duty ratio or frequency which direct the rotation controller to apply a strong or a weak braking force to the electric power generator; and a chopping signal selector that selects and outputs a chopping signal, such that at least either the timing of the start of a strong braking period, during which the chopping signal for strong braking is applied to the switch, or the timing of the start of a weak braking period, during which the chopping signal for weak braking is applied to the switch, is synchronous with a rotation detection signal associated with a rotor of the electric power generator, thereby controlling the electric power generator in a chopping manner according to the selected signal.
In this electronic device, according to the present invention, synchronizing the timing of starting a strong braking period with the rotor rotation detection signal, ensures that a strong braking force is applied immediately after the start of the strong braking period in response to the rotation detection signal. Thus, the control of the rotational speed can be performed in a quick and highly reliable fashion. On the other hand, if the timing of starting a weak braking period is synchronized with the rotor rotation detection signal, the timing of transition from the strong braking mode to the weak braking mode is set such that the transition occurs after the end of one period of a chopping signal for strong braking. This allows an improvement in the accuracy of the braking amount.
In the present invention, only the timing of the start of the strong braking period may be synchronized with the rotor rotation detection signal, or only the timing of the start of the weak braking period may be synchronized with the rotor rotation detection signal. Alternatively, the start timing may be synchronized with the rotor rotation detection signal for both the strong and weak braking periods.
In this case, the chopping signal selector preferably outputs the selected chopping signal such that either the weak braking start timing, at which time the chopping signal applied to the switch is switched from a strong braking chopping signal to a weak braking chopping signal, or the strong braking start timing, at which time the chopping signal applied to the switch is switched from a weak braking to a strong braking chopping, is synchronized with the chopping signal for strong braking or the chopping signal for weak braking. In the present invention, the control in the chopping manner refers to a controlling manner in which the electric path between the two terminals of the electric power generator is closed and opened using a control signal (chopping signal) having a frequency high enough compared with the rotational speed of the rotor of the electric power generator.
In this technique, because strong-to-weak braking transition or weak-to-strong braking transition occurs after the end of one period of a chopping signal for strong or weak braking, it is ensured that the chopping signal for strong or weak braking is applied over the specified entire period. Therefore, it is possible to control the braking amount at precise intervals equal to integral multiples of the unit period. Thus, the control accuracy can be further improved.
It is desirable that the chopping signal selector be capable of continuously outputting the chopping signal for strong braking over a period of time equal to or longer than one period of a reference signal.
This makes it possible to continuously apply a strong braking torque when the rotational speed of the electric power generator is very high. Thus, this technique allows quick response and high efficiency in the control of the rotation compared with the technique disclosed in Japanese Examined Patent Publication No. 7-119812, in which a braking-off operation is performed in each period.
The electronic device according to the present invention may further include a power supply, and first and second power supply lines for transmitting electrical energy generated by the electric power generator to the power supply for storage. The switch includes a first switch disposed between a first terminal of the electric power generator and the first power supply line, and a second switch disposed between a second terminal of the electric power generator and the second power supply line. The rotation controller controls the rotation period of the electric generator, such that one of the first and second switches is maintained in a closed state while the selected chopping signal is applied to the other switch, thereby turning it on and off.
In such an electronic device, not only the braking operation but also the operation of charging the generated electric power and the control of the rotation of the electric power generator are performed at the same time. Therefore, the circuit can be constructed using fewer components. Furthermore, the power generation efficiency can be improved by properly controlling the timing of closing and opening the respective switches.
It is desirable that the switches be formed of transistors. More particularly, the first switch preferably includes a first field effect transistor whose gate is connected to the second terminal of the electric power generator and a second field effect transistor which is connected in parallel to the first field effect transistor and which is turned on and off by the rotation controller. The second switch preferably includes a third field effect transistor whose gate is connected to the first terminal of the electric power generator and a fourth field effect transistor which is connected in parallel to the third field effect transistor and which is turned on and off by the rotation controller. With this arrangement, when the voltage of the first terminal of the electric power generator is positive with respect to the voltage of the second terminal, the first field effect transistor, whose gate is connected to the second terminal, is turned on (in the case where the first FET is of the p-channel type; the transistor is turned off if it is of the n-channel type), and the third field effect transistor, whose gate is connected to the first terminal is turned off (in the case where the third FET is of the p-channel type; the transistor is turned on if it is of the n-channel type). As a result, AC current generated by the electric power generator flows through a path including the first terminal, the first field effect transistor, one of the first or second power supply lines, the power supply, the other power supply line, and the second terminal.
On the other hand, when the voltage of the second terminal of the electric power generator is positive with respect to the voltage of the first terminal, the third field effect transistor, whose gate is connected to the first terminal, is turned on, and the first field effect transistor, whose gate is connected to the second terminal, is turned off. As a result, the AC current generated by the electric power generator flows through a path including the second terminal, the third field effect transistor, one of the first or second power supply lines, the power supply, the other power supply line, and the first terminal.
In the above operation, the second and fourth field effect transistors are alternately turned on and off in response to the chopping signal applied to the gates thereof. When the first and third field effect transistors are in the on-state, the current is passed regardless of whether the second and fourth field effect transistors are on or off, because the second and fourth field effect transistors are connected in parallel to the first and third field effect transistors, respectively. On the other hand, in the case where the first and third field effect transistors are in the off-state, the current is passed when the second and fourth field effect transistors are turned on by the chopping signal. Therefore, when one of the second and fourth field effect transistors is turned on by the chopping signal, both the first and second switches are turned on, and the two terminals of the electric power generator are connected to each other in the closed-loop state.
As a result, the electric power generator is braked in a chopping manner, such that the reduction in the electric power caused by braking is compensated for by the increase in the generated voltage obtained when the switches are turned off. Thus, the braking torque can be increased while maintaining the generated electric power at a certain level. This makes it possible to realize an electric device which can operate for a long period of time. Furthermore, because the rectification of the electric power generator is performed by the first and third field effect transistors whose gates are connected to the respective terminals, no comparator is required. This allows rectification to be performed using a simple circuit configuration. Furthermore, a reduction in the charging efficiency due to power consumption by the comparator is eliminated. Furthermore, because the field effect transistors are turned on and off using the terminal voltage of the electric power generator, the field effect transistors are turned on and off in synchronization with the polarity of the terminal voltage of the electric power generator. This results in an improvement in the rectification efficiency.
A preferable example of the electronic device according to the present invention is an electronically controlled mechanical clock including a time indication device which is rotated by the mechanical energy in connection with the electric power generator and which is controlled in terms of rotational speed by the rotation controller.
More specifically, the electronically controlled mechanical clock may include a mechanical energy source; an electric power generator, driven by the mechanical energy source connected to the electric power generator via an energy transmission device such as a wheel train, for generating electric power by means of induction and supplying resulting electrical energy; a time indication device connected to the energy transmission device; and a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator. The rotation controller may function in accordance with any of the previously described rotation controllers. In this electronically controlled mechanical clock, the braking torque applied to the electric power generator can be increased without causing a significant reduction in generated electric power. Therefore, it is possible to provide a high-precision clock which can operate for a long period of time.
Thus, in the electronically controlled mechanical clock in which the control of the rotation speed is important to accurately drive the hands, the present invention allows high accuracy of the rotation speed.
The application of the electronic device according to the present invention is not limited to the electronically controlled mechanical clock, but may be applied to a wide variety of electronic devices. In particular, the long operation period is advantageous in portable electronic devices such as analog quartz watches, digital watches, portable sphygmomanometers, portable telephones, personal handy phones, pagers, pedometers, calculators, portable personal computers, electronic notepads, PDAs (personal digital assistants), portable radio sets, various toys, music boxes, and electric shavers.
The present invention also provides a method of controlling an electronic device comprising a mechanical energy source, an electric power generator, driven by the mechanical energy source, for generating electric power by induction and supplying resulting electrical energy, and a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator. The method comprises applying a chopping signal, selected from at least two types of chopping signals which are different in at least either duty ratio or frequency and which direct the rotation controller to apply a strong braking force to the electric power generator, to a switch capable of connecting two terminals of the electric power generator in a closed-loop state, thereby controlling the electric power generator in a chopping manner according to the selected chopping signal.
In this control method, a braking force (damping torque) corresponding to the driving torque of the mechanical energy source can be obtained by applying a chopping signal selected from the two or more types of chopping signals which differ in at least either duty ratio or frequency and which are set for strong braking. This makes it possible to properly control the rotational speed of the electric power generator. Thus, the controllable operating range becomes wide, and the charged voltage can be increased. Therefore, it becomes possible to further increase the braking torque (damping torque) while more effectively suppressing the reduction in the generated electric power. Thus, an electric device that can operate for a longer period of time can be realized.
In another aspect of the invention, a method of controlling an electronic device is provided. The device comprises a mechanical energy source, an electric power generator, including a rotor, driven by the mechanical energy source, for generating electric power by induction and supplying electrical energy, and a rotation controller, driven by the electrical energy, for controlling the rotation period of the electric power generator. The rotation controller includes a switch capable of connecting two terminals of the electric power generator in a closed-loop state. The method comprises applying a chopping signal, selected from at least two types of chopping signals which are different in at least either duty ratio or frequency and which direct the rotation controller to apply either a strong or a weak braking force to the electric power generator, to the switch, wherein when a rotation detection signal associated with the rotor of the electric power generator is input, a chopping signal for strong braking is applied to the switch.
Also in this method according to the present invention, because the timing of starting a strong braking period is synchronized with the rotor rotation detection signal, it is ensured that a strong braking force is applied immediately after the start of the strong braking period in response to the rotation detection signal. Thus, the rotational speed can be controlled in a quick and highly reliable fashion.
The frequencies of the chopping signals set for strong and weak braking may be properly selected depending on the characteristics of the electric power generator to be controlled. Preferably, the frequency of the chopping signal for weak braking is in the range from 500 to 1000 Hz, and the frequency for strong braking is in the range from 10 to 100 Hz.
The chopping signals may be different in both frequency and duty ratio. In particular, to achieve a high-efficiency braking operation, it is desirable that the chopping signal for strong braking have a low frequency and a large duty ratio and the chopping signal for weak braking have a high frequency and a small duty ratio.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.